circadian englannista suomeksi
2000, Arnold Sameroff, ''et al''., ''Handbook of Developmental Psychopathology'', page 310
- The circadian clock is involved in the regulation of the diurnal sleep-wake cycle, ….
(quote-journal) (Weekend)|date=5 April 2014|page=W22|passage=Circadian clocks developed early in evolution in single-celled organisms, before the animal and plant kingdom split from one another. The original clocks probably functioned to protect the cells from damage induced by high UV radiation.